Method of making an artistic medium

ABSTRACT

The present invention is directed to a mineral-based coating composition that can be used on a wide range of substrate surfaces. The composition is comprised of a mineral extender, such as a delaminated hydrated aluminum silicate based clays, having an aspect ratio of about 11 to 1, water, a homopolymer polyvinyl acetate emulsion, a co-polymer polyvinyl acetate emulsion, an acrylic emulsion binder containing a metal dioxide and a buffering agent, a surfactant and a defloculant. Also provided is a method of preparing the mineral-based coating composition. The mineral-based coating composition may be applied to various substrate surfaces to form artistic medium surfaces. The present invention also provides a method of making an artistic medium surface using the composition of the present invention.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 08/867,963, filed onJun. 3, 1997 now U.S. Pat. No. 6,258,412; which is a divisional of U.S.Ser. No. 08/280,109, filed Jul. 25, 1994, now abandoned; which is acontinuation-in-part of U.S. Ser. No. 08/075,173, filed on Jun. 9, 1993,now abandoned, all of which are incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

This present invention is directed in general to a composition andmethods of manufacture of artistic media and, more particularly, to acomposition and methods of manufacture for clay-surfaced substrates.

BACKGROUND OF THE INVENTION

The use of clay as a medium for drawing or painting is not new.Countless millennia before mankind developed the ability to communicatein written or spoken language, drawings, in the form of petroglyphs,were used to express ideas and concepts. Unfortunately, these drawingsrequired large quantities of rock face or clay and were not portable.Also, erasure was a major problem.

To answer these deficiencies, canvas came into use several hundred yearsago, allowing the artist to paint pictures on lightweight, portablemedia. However, changing or erasing the painting once dry was difficultto nearly impossible, the canvas aged and rotted and had few of thestabilizing and texturing qualities attributable to clay.

In an effort to marry the desirable surface qualities of clay or otherrock with the light weight and portability of canvas, the prior art hasprovided an artistic medium termed “scratchboard” or “scraper board.”U.S. Pat. No. 2,523,650, which issued on Sep. 26, 1950, to Dickson, isrepresentative of such prior art and is directed to scraper and processboards capable of being engraved or carved. Dickson teaches depositionof a relatively thick layer of china clay and a bonding agent(water-soluble hide glue) over a comparatively rigid backing, such aspaste-board, ply-board or sheet metal. Deposition is by spraying.

Unfortunately, the scraper board disclosed in Dickson sufferssignificant shortcomings. First, the scraper board lacks the desireddegree of permanence in several respects. First, the surface isnon-permanent in the respect that the binder provided is optimized tobind the clay to the board and not the clay to itself. Therefore, theclay can erode as it is worked. Second, since the thin clay layer isrelatively inflexible, it tends to crack easily when the relativelyflexible cardboard is bent. This, too, is related to the strength of thebinder.

Third, artists not working just for reproduction purposes often wish tofix a completed work on an inflexible substrate for more permanentdisplay or storage, a necessity with fine art. Unfortunately, thecardboard backing of Dickson is not amenable to such mounting. Ifwater-base glues are used to bind the cardboard to the inflexiblesubstrate, the glue is liable to soak through to the clay layer,dissolving the gelatin glue and creating visible imperfections. Ifrubber cement is used instead, its hold may be released over timecausing the formation of large bubbles in the scraperboard, thus ruiningits mounting.

Fourth, since the binder of Dickson is water-soluble, it looses itsintegrity when wet, causing the dry clay surface to loose its bindingstrength and soften when wet, causing the clay surface to disintegratewhen subjected to water. As such, the clay surface is limited for somewatermedia techniques and photographic printing which requires totalimmersion of the media in water.

Fifth, the manufacturing process taught in Dickson (spraying of the clayonto the cardboard) limits the maximum size of the scraper board toabout 20×30 inches, thereby limiting the opportunity of an artist tocreate larger scale work using the a “scratchboard” technique.

Sixth, manipulation and reworking of the drawing or painting are limiteddue to the comparatively thin layer of clay on the soft cardboard base.

Seventh, cardboard-backed scratchboards have a tendency to crack whenbent in a curve of at most 12 inches in diameter in a dry environment,e.g., approximately 10% relative humidity. This is an absoluterequirement drum-type laser printers, representing the state of the artfor illustration reproduction.

Eighth, the surface of the Dickson board is pitted due to small bubblesformed in the spraying application of the wet clay. These pits becomeobvious defects in the drawing and painting processes and contribute tothe structural unsoundness of the surface.

Ninth, the manufacturing process does not lend itself to cost-effectivemass production. Several spray coats of clay must be applied to eachboard to achieve suitable clay thickness. This results in significantmanufacturing time and labor requirements.

The clay surface of Dickson allows minimal artistic manipulation. Whendrawing, the surface indents too easily when a sharp pencil is used,making it difficult to manipulate the line with subsequent scratching orabrading techniques. If bubbles are within the clay coating,manipulation can expose those bubbles, thus creating more surface pits.

Finally, spraying of the unrefined clay coating of Dickson onto thecardboard backing typically produces a fine mist of clay dust,containing silicates and quartz particles. Prolonged exposure to claydust created during manufacture or artistic use can cause silicosis dueto the presence of quartz crystal impurities in the unrefined clay.

Another scratchboard is disclosed in U.S. Pat. No. 1,923,483, whichissued on Dec. 7, 1927, to Glenn. Glenn teaches use of a backing sheetin the form of a dense, pressed paper board (sold under the brand names“Vehisote” or “Masonite”) upon which is deposited a shellac and a layerof mineral earth (principally magnesium silicate) in the form ofpurified talcum powder mixed with water into a paste. Deposition isperformed by heaping a mass of the paste onto the backing sheet andjogging the backing sheet until the paste covers substantially all ofthe sheet.

Although Glenn provides a shellac and a hard backing to overcome some ofthe above-noted problems, Glenn fails to provide for the flexibilityrequired for the board to run through a laser printer. Additionally, thejogging deposition method of Glenn is slow and tedious and can stillcause bubbles to become entrained in the coating. Finally, Glenn failsto provide a water-resistant binder to securely fix the paste to theshellac when the dry coating is subjected to application of water.

Finally, the prior art provided a scratchboard that consists of a claysurface composed of “6 tile Georgia kaolin” clay bound together and to a⅛ inch hardboard backing (again, Masonite) with a dilute adhesive. Thepermanence and physical durability was greatly increased by the claybeing applied to a rigid flat base (a hardboard), a factor which alsosolved the mounting as described above. The board was frame-ready, andneeds no glass for protection when sealed with an acrylic or varnishsealer. Provision of the rigid base and the dilute adhesive binderallowed the surface size to be extended up to 4 feet by 8 feet. Thisprior art scratchboard also provided a thicker clay layer, allowing morevigorous manipulation and reworking. Use of the dilute adhesive binderin the clay mix also gave much better water resistance, thus allowingthe use of waterbased painting on the scratchboard.

The 6 tile kaolin scratchboard thus solved most of the above-notedproblems with the earlier forms of scratchboard, but created in theirplace some new ones. First, the manufacturing process, never developedfor mass production, was similar to that taught in Dickson, i.e.,multiple spray coatings. This process was time and labor intensive, and,more important, produces small bubbles (on the order of 0.004-0.015inches in diameter) that dry in the clay layer, becoming unwantedsurface pits in the drawing, painting, and photographic print surfaceor, more insidiously, latent defects within the clay coating itself,becoming exposed only as the artist works. Manufacturing of 6 tilekaolin scratchboard required extensive refinishing to minimize thenumber of bubbles, resulting in considerable loss of material to the airand creating a risk of silicosis to workers exposed to atomized claymist containing quartz particles.

The spraying process employed in producing the prior art 6 tile kaolinscratchboard, coupled with the need to layer the applications, madeproduction cumbersome and expensive, and more important, rendered thesurface quality inadequate. The 6 tile kaolin scratchboard did notemploy a chemical to reduce surface tension. In many production runs ofthe 6 tile kaolin scratchboard, scrap rates of 50% or more have beenmeasured.

A second problem with the prior art scratchboard is that 6 tile kaolinhas a considerable amount of impurities, including iron compounds, thatgave it a slightly brown color, undesirable for most art work and photoprinting because of the imposed color and/or value on the imageproduced. This is particularly important for illustration purposes wherereproduction requires the whitest possible surface.

A third problem is that 6 tile kaolin, like the English-mined China clayof Dickson also contains a significant amount of quartz particles,presenting the health hazard of potential silicosis for those who aresubjected to prolonged exposure to the clay dust. Even artists whoseprincipal medium of expression includes unpurified kaolin-coated artboards prudently used respirators when scratching and abrading thesurface, still creating significant amounts of clay dust.

A fourth problem is that the existence of impurities and the lack of auniform particle size in 6 tile and English mined kaolin clays requiredmore liquid mixed in to arrive at a given viscosity, even with the useof a defloculant such as sodium silicate. More liquid in the applied mixrequired a longer drying time and resulted in more shrinkage of the claylayer during the drying process, giving rise to higher incidence ofcracking.

A fifth problem is that the unrefined kaolin clays required more bindingadhesive to coat the conglomeration of particle sizes and impurities fora given bonding integrity within the clay layer and between the claylayer and sealer coat.

The 6 tile kaolin scratchboard was sealed using waterproof adhesivebefore the clay layer was applied. This sealer, while attempting toprevent ion exchange from the hardboard to the clay layer and whilegiving a good bonding interface between the hardboard and the clay stillremained somewhat porous and wettable. This caused three problems: (1)the ion blockage was of questionable effectiveness over long periods oftime raising doubts as to whether the pH of the clay surface wouldremain unaffected, a point of considerable concern regarding pigmentstability of the artwork on the surface, (2) the porosity of the sealercaused, upon rewetting, a “show-through” of the dark hardboard surface,a change in color and value that even shows up through the finished claylayer when it is rewetted in the normal use of different water media,and (3) the porosity of the sealer created an “orange peel” surfacetexture in the dry clay coating requiring extensive sanding to achieve asmooth surface.

The artist was required to continually take this into account whenworking, remaining aware that the color of the brush stroke laid downappears darker because of show-through than it will be after the claysurface dries and returns to its original color and value. This becomesparticularly problematic in the photo printing process where control ofdelicate values while developing a print is crucial to the success ofthe photo in reproducing colors and shades with high fidelity.

Fifth, the resulting relatively brittle and non-uniform nature of theclay layer limited the 6 tile kaolin scratchboard's use to flat, rigidbases which cannot be used in drum-type laser printers. These laserprinters are in wide use among printers who reproduce illustrations.Also, the hard, brittle, non-uniform nature of the clay surface was aproblem when scratching or scraping with a pigment removal tool, makingeach stroke choppy instead of smooth and controlled, an essentialelement for an artist.

Other proposed artistic clay formulations that use either water-solublebinder hide glue or a polyvinyl acetate emulsion (PVA) as the solebinding agent also have several disadvantages. First, these formulationsdo not have the desired degree of permanence, which is defined herein asthe coating quality allowing it to maintain its integrity for 25 yearsor more under the normal treatment of art works. The permanence of anartistic medium can be affected in many ways.

For instance, the quality of adhesion may affect the permanence of theartistic medium. Adhesion is defined herein as the bond between thecoating and the substrate, whether in a wet or dry state. Artisticadhesive formulations that use water-soluble binder hide glue orpolyvinyl acetate emulsion as the sole binding agent have adequate dryadhesion to porous substrates such as cardboard or unsealed hardboardbut are limited to those substrates since neither has good adhesion whenthe coating is wetted in artistic applications of water media, or whenapplied to slick non-porous substrates such as primed/sealed hardboard,metal, plastic or glass. Application of these adhesives are thus limitedto coatings only to unsealed, porous substrates of organic fiber inorder to achieve a mechanical bond as the wet coating soaks in to theporous substrate.

Another factor that can affect permanence is in regard to particlebonding that, which is defined herein as the bond between the mineralparticles in the coating. Again, due to the use of hide glue or PVA asthe sole binding agent, the clay surfaces can exhibit a deficiency inresilience and flexibility, which, when struck or pressed on by a hardobject or subjected to bending stress may easily suffer indentations orcracking of the surface, respectively.

Yet another factor that can affect permanence is in regard to chemicalstability, which is defined herein as the coating's non-reactivity withother chemicals such as acids, bases, color pigments, pigment vehicles,varnishes, etc. In many conventional applications, the coating is notchemically isolated from the substrate of acidic wood fiber in thecardboard and hardboard substrates, which overtime allows the passage ofacidic ions from the substrate to the coating. Moreover, the prior artadhesive formulations, which typically have a pH of approximately4.0-5.0, are acidic in nature and therefore chemically active. Due tothe deficiencies of the adhesives typically used as discussed above, itis not feasible to apply these coatings to slick, sealed, non-poroussubstrates. Therefore, the acidic ions are left un-inhibited to migrateinto the pigment and compromise the integrity of some color pigments andpigment vehicles causing a change in color over time, and in turn,compromising the integrity of art work on the surface.

Still another factor that can affect permanence is in regard toresistance to ultra-violet (UV) light degradation, which is definedherein as the coating's ability to maintain its integrity of color andbond strength under prolonged exposure to UV light rays. Theconventional formulations using hide glue as the adhesive may experienceundesirable levels of degradation since the adhesive is of organicorigin, and thus subject to UV light degradation. Moreover, inapplications involving unrefined kaolin, which is a clay having a lightbrown color due to organic impurities, the unrefined kaolin graduallybleaches to a lighter color as the UV light reacts on the organicimpurities, thus compromising the original values and color as renderedby the artist. Furthermore, this same use of an unrefined kaolin, whichhas d wide range of clay particle sizes, requires more binder for agiven bond strength.

The second disadvantage of conventional artistic formulations regardsthe durability in use, which is defined herein as the ability of thecoating to maintain its original qualities under normal conditions ofartistic use, including coating flexibility, coating resilience,rewetability, and particle bonding. Durability in use may further bedefined by ASTM standard D-3290 as “the ability to resist the effect ofwear and tear in performance situations.”

As was the case with permanence characteristics, there are severalfactors that may also affect durability of use, for example, coatingflexibility, which is defined herein as the ability of the coating toresist cracking or flaking when bent either in compression or tension.In proposed artistic mediums using hide glue or PVA in conjunction withunrefined clays, the coating produced is a relatively brittle coatingwhich experiences cracking when bent to a diameter of approximately 12inches or less under dry environmental conditions of 10% humidity orless. As used herein, an unrefined clay is one which is processed by adry air alutriation process, has particles ranging in size from 0.2microns up to 44 microns and contains impurities such as freecrystalline silica. In physical abuse situations, not uncommon in thenormal handling of an art surface, accidental bending of the substratewould thus result in its degradation due to surface cracking. Thislimitation in flexibility would also prevent the coating's effective usein the art reproduction machine known as a laser printer in which theart work must be fed through the machine on a roller of 10″ diameter.

Another factor that affects durability in use is in regard to coatingresilience or hardness, which is defined herein as a coating's ability,whether wet or dry, to resist indentation from the force of a hard,sharp object such as a pencil lead or ink pen on the surface. The priorart medium having a soft, non-resilient surface is relatively easy toindent with normal pencil pressure on the surface and extremely easy todo so on a wet surface. Thus, on a surface intended to be drawn upon anderased multiple times, the indented line would remain visible, thuslimiting these surfaces in the amount of robust reworking the artistcould achieve.

Another factor affecting durability in use is in regard to the particlebond quality, which is defined herein as bond strength between clayparticles under both wet and dry conditions. The prior art which useshide glue, a water soluble binder, does not maintain an acceptableparticle bond when wetted, thereby preventing effective artisticmanipulation of pigment when the surface is wet as commonly occurs withwater media applications. Further, immersion in water for a long periodof time totally disintegrates this coating because of the watersolubility of the glue. Proposed artistic media formulations which usePVA, a water miscible binder, provides a bond stronger than that of hideglue but one, which, when wet can still be broken down by physicalmanipulation of the surface such as a brush stroke on the wet surface.This undesirable physical characteristic causes clay particles todisengage from the surface and mix with the color pigment of the brushstroke changing its color intensity. Further, this deficiency preventsthe use of these media as a surface onto which a photo emulsion may beplaced to print a photo due to the requisite developing, fixing, andwashing baths of normal photo developing.

Yet another factor affecting durability is in regard to toolability,which is defined herein as the quality of the coating which allowsconsistent, smooth working of the surface with scratching, scraping, orabrading tools. The prior art media which uses hide glue as a binderprovides a relatively soft, non-resilient coating surface which must bescratched or scraped in a delicately conservative manner so as not tocut too deeply thereby ruining the surface. These prior art mediatypically use unrefined kaolin that provides a relatively brittlesurface, as noted before. In addition however, due to the clumping ofparticles in an unrefined clay, the coating exhibits hardness (i.e.,density) inconsistencies in the surface. This, in turn, causesinconsistent tooling results, an important factor to the artist whoneeds as much tool control as possible to consistently render accuratepigment removal strokes, as well as an important factor in manufacturingquality control regarding surface dressing procedures. This deficiencyalso causes inconsistencies in the way the surface absorbs liquid-bornepigments causing ‘spotting’ upon applying certain paints to the surface.

A third disadvantage regards art rendering problems, which is definedherein as qualities of the coating surface which create difficulties inrendering artwork on the surface as well as shortcomings in the finalpresentation of the finished work. Again, several factors affect artrendering characteristics, for instance, surface pitting. Many prior artapplications use a spraying technique to apply the coating mix to thesubstrate which entraps many small bubbles in the coating layer. Whenallowed to air dry, these wet bubbles become air pockets throughout thecoating layer with some bubbles being visible on the surface and somebeing embedded in the layer. In the normal application and removal ofcolor pigment, the deep pits become filled with pigment making itimpractical to totally scrape them clean for an unblemished highlightarea if desired by the artist. Further, the pitting creates problems inconsistent tool use, for example, by catching the point of an ink pen asa line is being executed, or by making a scraping stroke rough anduneven.

Another factor affecting art rendering is in regard to value change uponwetting, defined herein as the darkening of the clay surface when wateris applied due to show-through of the dark substrate. In artistic mediumusing conventional adhesion formulations, a sealer of light color toblock this wet show-through cannot be used, thereby making it difficultfor the artist to discern what the true value and color of a brushstroke will be when it later dries.

Still another factor affecting art rendering is in regard to coatingcolor, which is defined herein as the color imparted to the surface bythe clay itself. Typical clay-based artistic mediums use unrefined clayswhich give a light brownish cast (e.g., 6 tile kaolin clay) or a coldblue-white color (e.g. the Dickson clay) due to the presence of iron andorganic impurities, which is normally considered undesirable forillustration renderings since the whitest possible surface is requiredfor effective reproduction.

A fourth disadvantage is the health hazard created by the use of theconventional clay-based artistic mediums. As previously stated, typicalclay-based artistic mediums use unrefined kaolin clays that containsignificant amounts of quartz crystals. As the artist works the medium,these quartz crystals may be inhaled along with the clay dust created bythe abrasion or scratching techniques or by the air-borne sprayingapplication techniques common to the art. Over a period of time, theseharmful particles can accumulate in the lungs, thus posing a risk ofdeveloping the respiratory diseases.

Thus, what is needed in the art is a coating and method of manufacturingthe same that overcomes all of the above-noted disadvantages of theprior art.

SUMMARY OF THE INVENTION

To address the deficiencies of the prior art, it is a primary object ofthe present invention to provide a mineral-based coating compositioncomprising a mineral extender, water, polyvinyl acetate emulsion and anacrylic polymer binder. In a preferred embodiment, the mineral extendercomprises from about 20% to about 36% of the composition's total weight,and in a more preferred embodiment, the mineral extender comprises fromabout 30% to about 32% of the composition's total weight and ispreferably a delaminated clay. The water preferably comprises from about40% to about 50% and more preferably comprises from about 44% to about46% of the a composition's total weight. The polyvinyl acetate emulsionpreferably comprises from about 16% to about 24%, and more preferablycomprises from about 19% to about 20% of the composition's total weight.The acrylic polymer binder preferably comprises from about 2% to about5%, and more preferably from about 3% to about 4% of the composition'stotal weight.

Preferably, the mineral extender is selected from the group consistingof kaolin clay, mica, talc, montmorillonite, atapulgite, illite,bentonite or halloysite, and more preferably is a hydratedaluminum-silicate kaolin clay having an aspect ratio of about 11 to 1.

In a preferred embodiment of the present invention, the polyvinylacetate emulsion is comprised of a homopolymer polyvinyl acetateemulsion and co-polymer polyvinyl acetate emulsion with the homopolymerpolyvinyl acetate emulsion preferably comprising from about 13% to about18%, and more preferably from about 14% to about 15% of thecomposition's total weight and the co-polymer polyvinyl acetate emulsionpreferably comprising from about 3% to about 6%, and more preferablyfrom about 4% to about 5% of the composition's total weight.

In another aspect of the preferred embodiment of the present inventionthe acrylic polymer binder further comprises a pigment and a bufferingagent wherein the pigment is preferably a Group II metal dioxide,preferably selected form the group consisting of titanium dioxide,zirconium dioxide and hafnium dioxide and more preferably is titaniumdioxide with the buffering agent being calcium carbonate.

In yet another aspect of the preferred embodiment of the presentinvention, the mineral-based surface coating composition furthercomprises a nonfoaming surfactant and a defloculant wherein thedefloculant is a sodium silicate.

In another aspect of the present invention, a method for making thecomposition of the present invention is also provided. The steps ofmaking the invention comprise, (a). preparing a binder mixture by mixingapproximately 3 parts per unit volume the homopolymer polyvinyl acetatewith approximately 1 part per unit volume of the co-polymer polyvinylacetate in a mixing container; (b). preparing a binder/water mixture byadding, for each approximate 1 part per unit volume of the bindermixture, approximately 2⅔ parts per unit volume of hot water ofapproximately 110° F.; (c). separating out ⅓ by volume of thebinder/water mixture into a separate container, thereby leaving aremaining ⅔ by volume of the binder/water mixture in the mixingcontainer; (d). preparing a mineral/binder/water mixture by addingapproximately 50 lbs. of mineral extender to the remaining ⅔ by volumeof the bind/water mixture; (e). adding to the mineral/binder/watermixture approximately 6 lbs. of an acrylic binder emulsion; and (f).adding to the mixture obtained in step (e). the ⅓ of binder/watermixture obtained in step (c). Preferably, the mineral extender isselected from the group consisting of kaolin clay, mica, talc,montmorillonite, atapulgite, illite, bentonite or halloysite, and morepreferably is a hydrated aluminum-silicate kaolin clay having as aspectratio of about 11 to 1.

In a preferred embodiment of the method of making the composition, thepolyvinyl acetate emulsion is comprised of a mixture of two differenthomopolymer polyvinyl acetate emulsions with the homopolymer polyvinylacetate emulsion preferably comprising from about 13% to about 18%, andmore preferably from about 14% to about 15% of the composition's totalweight. In this same embodiment, the co-polymer polyvinyl acetateemulsion preferably comprises from about 3% to about 6%, and morepreferably from about 4% to about 5% of the composition's total weight.

In another aspect of the preferred embodiment of the method of makingthe composition, the acrylic polymer binder further comprises a pigmentand a buffering agent wherein the pigment is a titanium dioxide and thebuffering agent is calcium carbonate.

In yet another aspect of the preferred embodiment of the method ofmaking the composition, the process further comprises adding 0.04 lbs ofa non-foaming surfactant to the mixture obtained in step (e) and addingapproximately 1.36 lbs. of a defloculant, which is preferably sodiumsilicate to the mixture obtained in step (e).

In yet another aspect of the present invention, there is provided apreferred method of making an artistic medium using the composition ofthe present invention. The method steps of making the artistic mediumcomprise: (1) providing a mineral-based coating composition comprising amineral extender comprising from about 20% to about 36% of themineral-based coating composition's total weight, water comprising fromabout 40% to 50% of the mineral-based coating composition's totalweight, a polyvinyl acetate emulsion comprising from about 16% to about24% of the mineral-based coating composition's total weight and anacrylic polymer binder comprising from about 2% to about 5% of themineral-based coating composition's total weight; (2) applying a sealingcoat to a backing material; (3) applying the mineral-based coatingcomposition over the sealing coat; and (4) drying the appliedmineral-based coating composition by heating the medium.

In a preferred embodiment, the mineral extender may be selected from thegroup consisting of kaolin clay, mica, talc, montmorillonite,atapulgite, illite, bentonite and halloysite. More preferably, however,the mineral extender is a hydrated aluminum silicate kaolin clay whereinthe kaolin clay has an aspect ratio of about 11 to 1.

In another aspect of the invention just described, the method of makingthe artistic medium further comprises the step of drying the surfacesealing coat prior to the step of applying the mineral-based coatingcomposition.

In yet another aspect, the method of making an artistic medium furthercomprises the step of surface dressing the mineral-based coating, and inanother aspect, the method further comprises the step of applyingadditional optional topical coatings over the mineral-based coating.

The substrate or backing material to which the coating may be appliedmay be flexible and may further be hardboard, glass, metal, plastic oracrylic plastic. In those instances where the substrate is flexible, themedium may even be used in conjunction with a laser printer.

In another aspect of the preferred embodiment of making the artisticmedium, the polyvinyl acetate emulsion is comprised of a mixture of twodifferent homopolymer polyvinyl acetate emulsions. Preferably, thehomopolymer polyvinyl acetate emulsion comprises approximately fromabout 13% to about 18%, and more preferably from about 14% to about 15%of the mineral-based coating composition's total weight, and theco-polymer polyvinyl acetate emulsion preferably comprises from about 3%to about 6%, and more preferably from 4% to about 5% of themineral-based coating composition's total weight.

In another aspect of the preferred embodiment of making the artisticmedium, the acrylic polymer binder further comprises a pigment and abuffering agent wherein the pigment is preferably a titanium oxide andthe buffering agent is calcium carbonate.

In yet another aspect of the preferred embodiment of making the artisticmedium, the mineral-based coating composition further comprises anonfoaming surfactant or a defloculant wherein the defloculant is sodiumsilicate.

In yet another aspect of the preferred embodiment of making the artisticmedium, the mineral-based coating composition further comprises watermiscible perlite and the step of making further includes the step ofapplying a perlite layer over the mineral-based coating composition.

Another aspect of the preferred embodiment of making the artistic mediumincludes the step of applying a layer of photosensitive material overthe mineral base coating composition.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention so that the detailed description ofthe invention that follows may be better understood. Additional featuresand advantages of the invention will be described hereinafter which formthe subject of the claims of the invention. Those skilled in the artshould appreciate that the conception and the specific embodimentdisclosed may be readily utilized as a basis for modifying or designingother structures for carrying out the same purposes of the presentinvention. Those skilled in the art should also realize that suchequivalent constructions do not depart from the spirit and scope of theinvention as set forth in the appended claims.

The family of art surfaces within the scope of the present invention allhave the common feature of being non-paper, rigid based surfaces, coatedwith a clay preparation of at least 12 mils thick. To the naked eye, itis these characteristics which differentiate the products from otherprior art surfaces. From a technical perspective, however, the productattributes can be broken down into the following four major categories.

1) non-paper, rigid backed surface

pressed wood surface such as masonite or equivalent

a broad range of synthetic materials any of which will support a coatingapplication of 12 mils thickness.

2) clay-based coating which contains strong binding characteristics, yetwhich offers flexibility in bending.

strength of binding agent allows surface to be immersed in water withoutdissolving or damaging coating.

3) thick coating applied to the backing no less than 12 mils thick.

this allows approximately 25 plus cuts or erasures before exposing thesurface.

4) sealant separating the coating and the backing material.

prevents reaction of backing and coating mixture, thus rendering a pHneutral surface, a critical feature for an artist.

prevents show-through of the underlying backing color.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates an isometric cutaway view of the prior art scraperboard as taught in the patent to Dickson;

FIG. 2 illustrates an isometric cutaway view of the prior art 6 tilekaolin scratchboard;

FIG. 3 illustrates an isometric cutaway view of the prior art scraperboard of FIG. 1 when bent;

FIG. 4 illustrates an isometric cutaway view of the prior art scraperboard of FIG. 1 when being mounted to a rigid substrate;

FIG. 5 illustrates an isometric cutaway view of the prior art scraperboard of FIG. 1 with particular emphasis on undesirable surfacecharacteristics;

FIG. 6 illustrates an isometric cutaway view of a scratchboard with thecoating composition of the present invention applied thereon;

FIG. 7 illustrates an isometric cutaway view of the coating compositionof the present invention as modified to function on a pastel board;

FIG. 8 illustrates an isometric cutaway view of the coating compositionof the present invention as modified to function on a watermedia board;

FIG. 9 illustrates an isometric cutaway view of the coating compositionof the present invention as modified to function on a photographicboard;

FIG. 10 illustrates an isometric cutaway view of the coating compositionof the present invention as modified to function on a laser printerboard; and

FIG. 11 illustrates a block diagram of the method of manufacturing theartistic media of the present invention.

DETAILED DESCRIPTION

Reference is initially made to FIGS. 1 through 5. FIG. 1 illustrates anisometric cutaway view of the prior art scraper board as taught in thepatent to Dickson, FIG. 2 illustrates an isometric cutaway view of theprior art 6 tile kaolin scratchboard, FIG. 3 illustrates an isometriccutaway view of the prior art scraper board of FIG. 1 when bent, FIG. 4illustrates an isometric cutaway view of the prior art scraper board ofFIG. 1 when being mounted to a rigid substrate and FIG. 5 illustrates anisometric cutaway view of the prior art scraper board of FIG. 1 withparticular emphasis on undesirable surface characteristics.

Turning now to FIG. 1, shown is a relatively non-rigid cardboard backingmaterial 10 over which a thin clay coating 11 of unrefined, non-kaolinclay that has a water soluble hide glue, a defloculant and apreservative has been directly deposited by spraying. There is noimpermeable sealer layer isolating the clay from the substrate, which isa wood fiber based cardboard of substantial flexibility and significantacid content. As previously mentioned in the Background of theInvention, the deficiencies of this configuration may be categorizedwith reference to the following qualities previously discussed.

With respect to permanence, the use of an unrefined, non-clay, which hasa wide particle size range and that is bound only with a water solublehide glue to a non-rigid, relatively fragile, unsealed, organicfiber-based cardboard, provides an art substrate that is suspectable tophysical degradation over time. The degradation may be due to theeffects of UV radiation, to accidental abuse of bending and indentation,or to the deleterious effect that coating acid content may have onpigment and pigment vehicle.

With respect to durability in use, due to the qualities of theconfiguration described above, the prior art is subject to physicaldegradation during the execution of art work: (1) when a sharp pencil orpen indents the soft surface while making a line, (2) when repeatedapplications of water in water media renderings of all kinds dissolvethe particle bond thereby allowing previously applied pigment to liftoff or clay particles to mix into the color, or (3) when the artistattempts to physically manipulate the wetted clay layer as with abrasiveor scratching strokes to remove pigment.

With respect to art rendering, due to the qualities of the configurationdescribed above, effective art rendering is compromised by the presenceof pits which can catch the point of a pencil or ink pen as a line isbeing rendered and can diminish artistic control over a scratching orabrading stroke used to create highlight detail by making it rough anduneven. Again the presence of indentations caused by previously executedlines in the relatively soft surface can prove problematical in removingthe lines or drawing over them.

With respect to health hazard, due to the use of unrefined clay whichcontains significant amounts of quartz crystals, any dust producingoperations on the surface such as abrading or scratching would pose athreat over time of developing the respiratory disease, silicosis.

Turning now to FIG. 2, shown is a hard, relatively inflexible, unsealedbacking material 20, such as Masonite, upon which is deposited a layerof clay mixture 21 consisting of unrefined kaolin clay of a wideparticle size range bound only with a PVA is deposited.

As previously mentioned in the Background of the Invention, thedeficiencies of this configuration may likewise be categorized withreference to the same qualities previously discussed above.

With respect to permanence, the above described configurationcompromises the ability of the coating to maintain its integrity overlong term exposure since the UV radiation bleaches out the organicimpurities, which in turn changes the original color and values of theart work as originally executed by the artist. Additionally, however,the coating cannot be applied to an impermeable slick substrate becauseof the deficiencies in adhesive strength of the binder as previouslydiscussed. Thus, without being able to use a sealer to isolate thesubstrate from the coating, the acid from the acid bearing organic fibersubstrate may leach into the coating through acidic ion absorption andeventually degraded the pigments and pigment vehicles. Also, the lack ofa buffering agent in this configuration results in a coating of acidicpH, again, a property deleterious to long-term art preservation.

With respect to durability, the relatively soft, non-resilient surfacesuffers indentation during the normal use of pencils and pens in artrendering. Also, due to the deficiency in particle bond strength whenwet, the coating suffers dissolution of the particle bond under physicalmanipulation conditions of normal art rendering.

With respect to art rendering, the light brown color of the clay bodyimparts its color and value to colors laid down by the artist. Also lackof a white primer/sealer under the clay results in show through of thedark hardboard surface when the surface is wetted, again impartingconsiderable color and value change to a brush stroke. Also the pittedsurface causes art rendering problems noted above.

With respect to health hazard, the use of an unrefined Kaolin containingsignificant amounts of quartz crystals with the corresponding threat ofsilicosis.

Turning now to FIG. 3, shown is the scraper board of FIG. 1 when bent.The backing material 10 is flexible, but the clay coating 11 isinflexible and poorly bound to the backing material 10. Therefore, whenthe scraper board is bent, cracks 30 are created in the clay coating 11.These cracks are common in the Dickson scraperboard due to the fragilenature of a thin clay layer on the flexible and flimsy cardboard.Increased durability of the scratchboard of the present invention ispartially due to an increase in uniform clay thickness on a hard board.Furthermore, pits are a result of exposure of bubbles that have come tothe surface either in the manufacturing process or in the scraping orsanding of the surface. Bubbles are a result of three production faults:(1) the spraying process, wherein the clay mixture is sprayed on thebacking material (individual clay droplets forming bubbles when theyimpact the clay surface), (2) the lack of the use of a surfactant toreduce the surface tension, (3) the use of a non-uniform clay particleclay mixture and (4) lack of oven drying that tends to burst bubbles.

Another problem with the Dickson scraper board more thoroughly describedin the Background of the Invention is that it is difficult to mount thecardboard-backed scraper board to a rigid board for permanent display orstorage. This is illustrated in FIG. 4, wherein a rigid board 40 must bebound to the cardboard backing material 10 by use of a glue 41. If theglue 41 is water-based, water can leach through the cardboard backingmaterial 10 to the clay coating 11 above, causing harm to the artist'swork. Alternatively, if the glue is non water-based, such as rubbercement, the glue can lose contact with the cardboard backing material 10over time, causing warping of the cardboard backing material 10 andbubbles to appear between the cardboard backing material 10 and therigid board 40.

Turning now to FIG. 5, the spraying process is shown to create bubblesin the clay coating 11 because air is introduced in the misting process.These small, often invisible bubbles sometimes coalesce during drying toproduce larger bubbles that may affect art quality. These bubbles mayrise to the surface to cause pits 50 or may remain buried to causeinternal air pockets or bubbles 51.

Bubbles can be minimized through use of a surfactant in the claymixture. Surfactants work by reducing the surface tension of themixture, thereby reducing the tendency of the mixture to entrain airpockets. By failing to use a surfactant, the surface tension retains thebubbles created during deposition instead of allowing them to escape orburst.

Disparate clay particle sizes found in unrefined clays promote higherviscosity in the clay solution for a given amount of liquid, which inturn creates higher surface tension by introducing very small particlesand shortening storage life by introducing heavy particles that settleout in the solution. Mixing such a solution does not improve theviscosity and, in fact, increases the number of bubbles trapped withinthe solution. Thus, the degree to which the particles of the clay arevaried also bears on the problem of air entrainment.

Cracks are present in the scraper board of Dickson due to the fragilenature of the thin clay layer on the flexible cardboard. Increaseddurability of the scratchboard of the present invention is partially dueto an increase in clay thickness. The use of a curtain coater allows avery thick layer (e.g. at least approximately 20 wet mils) of claymixture to be deposited on the sealer coat while retaining high surfacequality.

Pits are a result of exposure of bubbles which have come to the surfaceeither in the manufacturing process or in the scraping or sanding of thesurface. Bubbles that fail to rise to the surface can be potentiallymore harmful because they are not apparent to an inspector at the timeof manufacture and therefore may be found in scratchboards that havepassed quality control, only to be found wanting in the artist's eyes.Furthermore, manipulation by the artist may uncover these bubbles,making the artist's work more difficult and compromising the qualitiesof the surface. The number of erasures that the artist can make and thevigor with which the artist can manipulate the board are limited due tothe thinness of the clay layer.

Prolonged exposure to the clay dust in the manufacturing process and/orartistic use can cause silicosis due to the presence of quartz crystalimpurities in the unrefined clay. Resurfacing of old boards causesairborne silicates which can lead to silicosis over prolonged exposure,thus making the scratchboard of the present invention more ecologicallysound.

Turning now to FIG. 6, illustrated is an isometric cutaway view of ascratchboard having the coating composition of the present inventionapplied thereon. Shown are a rigid backing material 60. The rigidbacking material 60 may be a hardboard, which is defined herein as aboard constructed of pressed individual fibers. Hardboard can be ofsoftwood (conifers, for instance) or hardwood (oak or beech, forinstance). Hardwood fiber is a preferable substrate on which the coatingcomposition of the present invention may be applied for two reasons.First, hardwood has a shorter fiber length; therefore the surface ismore uniform. Second, hardwood is less acidic than softwood; thereforethere is a lower chance of chemical reactions between the hardboardbacking material and the sealer coat.

A sealer coat 61 is applied over the backing material 60 to chemicallyand physically isolate the backing material from a clay mixture 62deposited over the sealer coat 61.

The mineral-based coating composition of the present inventionpreferably comprises a mineral extender, water, polyvinyl acetateemulsion (PVA), and an acrylic polymer binder. The mineral extender maybe any type of mineral silica-based composition such as those used inrefractories or ceramics. The mineral extender is preferably delaminatedand comprises from about 20% to about 36% and more preferably from about30% to about 32% of the coating composition's total weight andpreferably has an aspect ratio, i.e., length to thickness of theplatelets, of 11 to 1. For example, the mineral extender may be akaolinite, talc, mica, montmorillonite, atapulgite, illite, bentonite orhalloysite. More preferably, however, the mineral extender is adelaminated hydrated aluminum silicate kaolin clay that is screened to aparticle size ranging from about 0.4 microns to about 6 microns with anmedian particle size of about 2 microns. The kaolin clay is of abrighter white than previously used. This is important for illustrationpurposes that requires the whitest possible artistic surface.

The refinement process removes organic and inorganic impurities from theclay body giving a whiter color and gives an advantage in art renderingby giving colors applied to the surface a truer hue, thereby offeringgreater contrast for reproduction of art work. The use of the refineddelaminated kaolin, which, unlike the impurity laden, non-delaminated 6tile kaolin that tends to bleach out to a lighter color over time,remains unchanged in color. This refinement provides an advantage inpermanence with respect to the maintenance of original color and valuewhen executed by the artist.

As is known, most clays are comprised of layered platelets that areadhered together to form thicker particles of the clay. The delaminationprocess, which is a water wash process, breaks up these layeredplatelets into much thinner platelets, which facilitates screening touniform particle size, and provides for consistent quality controlregarding density variation, flexibility and general uniformity of thesurface. In regard to toolability, it provides smooth, consistenttooling such as in scratching or scraping the surface in pigment removalor in surface dressing the homogenous coating to give it a surfacetexture or surface of an even level. Further, the homogenous dispersalof like particles throughout the coating provides a higher degree offlexibility and even color pigment acceptance in art rendering withoutspotting due to irregularities in surface density.

While the delamination and screening to uniform particle size isintegral to the above qualities in art rendering, it was alsounexpectedly found to greatly aid the application process in regard to:(1) coating drying time in that approximately ⅓ less water is requiredfor total wetting of the clay particles and thus for a given viscosityof coating mix, (2) binder quantity reduction by approximately ⅕ due inlike manner to the reduction in total particle surface area roverage,and (3) reduction of surface tension of the coating liquid caused bylarge number of very small particles in that fewer bubbles are entrainedin the mix during application. Those that do remain easily rise to thesurface of the coating and burst as the coated substrate passes throughthe forced air drying ovens, thus resulting in a dried surface withoutpitting—a marked quality improvement over the prior art.

Preferably, the water component, which preferably has a pH ofapproximately neutral to slightly basic (e.g. a pH range ofapproximately about 7.0 to about 8.5), comprises from about 40% to about50%, and more preferably from about 44% to about 46% of thecomposition's total weight.

The polyvinyl acetate emulsion (PVA) preferably comprises from about 16%to about 24%, and more preferably from about 19% to about 20% of thecomposition's total weight. Preferably, the PVA is comprised of ahomopolymer polyvinyl acetate emulsion that ranges from about 13% toabout 18%, and more preferably from 14% to about 15% of the coatingcomposition's total weight and a co-polymer polyvinyl acetate emulsionthat comprises from about 3% to about 6%, and more preferably from about4% to about 5% of the coating composition's total weight. Thehomopolymer polyvinyl acetate emulsion component provides a waterabsorptive bond matrix between the clay particles giving the coatinggood absorptive qualities.

Moreover, the homopolymer polyvinyl acetate emulsion used in the presentcomposition is preferably an opaque liquid that is white in color and aslight acetic odor, miscible in water, has a freezing point of 0° C., aboiling point of about 100° C., a vapor pressure of 17.5 mm Hg at 20°C., a vapor density of 0.62 (water), air=1, a specific gravity of fromabout 1.08 to about 1.10, a pH of from about 4.0 to about 5.5 at 25° C.and a volatile organic content of approximately 3 gms/liter, less water.An example of the homopolymer that is commercially available is “ELMER'SGLUE-ALL”, product number E960, manufactured by Borden, Inc. at 180 EastBroad Street, Columbus, Ohio 43215.

The co-polymer polyvinyl acetate emulsion used in the presentcomposition gives improved adhesion to the substrate of impermeablesealed hardboard as well as to alternative substrates such as primedmetal, plastic and glass, thus enhancing the permanence qualities of thecoating. The co-polymer also improves upon the qualities of flexibilityand toolability affecting permanence, durability and art rendering asdefined above. Additionally, the co-polymer was found to strengthen thebond matrix, offering improved flexibility and better wettingresistance. The preferred co-polymer acetate emulsion used in thepresent composition is milky white in color with a mild odor, soluble inwater, has a vapor density of less than 1 (water), a specific gravity ofabout 1.095, a pH of about 5.0, a boiling point of about 100° C. and avolatile organic content of approximately 48% by weight. An example ofthe co-polymer that is commercially available is “WELLBOND ADHESIVE”manufactured by Frank T. Ross and Sons Limited at 6550 Lawrence avenueEast, West Hill, Ontario, Canada M1E 4R5.

The preferable acrylic polymer binder used in the present composition isa white, opaque thick paste Gesso and preferably comprises from about 2%to about 5%, and more preferably from about 3% to about 4% of thecomposition's total weight. The acrylic polymer binder furtherpreferably comprises a white pigment, such as a Group II metal dioxidesuch as titanium dioxide, zirconium dioxide or hafnium dioxide and abuffering agent, such as calcium carbonate. The pigment whitens theresulting surface, thereby improving upon the art rendering by reducingthe effect a slightly colored ground has in color application and byproviding greater value contrast in artwork reproduction. The calciumcarbonate raises the pH of the coating to approximately 7.0 to 7.5,neutral to slightly basic. This pH enhances the permanence and chemicalstability of the composition by retarding acidic degradation of colorpigments or pigment vehicles over the life of the art work. Moreover,the slight basicity provides a buffering action that counteracts theabsorption of acid from environmental sources. Examples of the acrylicbinder used in the present composition that are commercially availableare: (1) “UTRECHT ARTIST GRADE GESSO” manufactured by UtrechtManufacturing Company at 33-35th Street, Brooklyn, N.Y. 11232; (2)“GRUMBACHER PROFESSIONAL GESSO”, manufactured by Grumbacher at 100 NorthStreet, Bloomsbury, N.J. 08804-0068; and (3) “LIQUIATEX ACRYLIC GESSO”,manufactured by Binney & Smith at 1100 Church Lane, Easton, Pa. 18042.

The acrylic polymer binder component provides an improved particlebonding matrix that renders the bond less subject to particle bonddisintegration upon wetting or upon physical manipulation while wet andthus, positively affects permanence, durability in use and artrendering. Moreover, it improves adhesion to impermeable slicksubstrates such as sealed hardboard and to alternative substrates suchas metal, plastic and glass.

In addition to the components discussed above, the coating compositionmay also include the additional components of a surfactant or adefloculant. The surfactant, a non-foaming wetting agent, lowers thesurface tension of the coating mix, thereby allowing bubbles that dobecome entrained in the coating layer upon application to more easilyburst when passed through the forced air drying ovens, thus directlyaffecting art rendering by eliminating pits. When present in the coatingcomposition, the surfactant preferably comprises from about 0.03% toabout 0.04% of the coating composition's total weight.

The defloculant, which is preferably a sodium silicate, facilitatesapplication and speeds the dry time of the coating by reducing theamount of water needed to bring the coating mix to a given viscosity.Additionally, it creates a uniform dispersal of clay particlesthroughout the coating, thus improving upon uniformity of the surfaceand toolability. When present in the coating composition, thedefloculant preferably comprises from about 0.80% to about 0.9% of thecoating composition's total weight.

A preferred embodiment of the coating composition of the presentinvention may be prepared in accordance with the following preferredmethod of preparation.

In a mixing container, prepare a binder and water mixture by mixingapproximately 3 parts per unit volume of the homopolymer polyvinylacetate emulsion with approximately 1 part per unit volume of theco-polymer polyvinyl acetate, i.e., about 23.67 lbs of the homopolymerpolyvinyl acetate emulsion with about 7.56 lbs of the co-polymerpolyvinyl acetate. To each approximate 1 part per unit volume of bindermixture added 2⅔ parts per unit volume, i.e., about 72.48 lbs, of hotwater at 110° F. and slowly mix in the hot water. This should bethoroughly agitated until there is consistent dispersion and suspensionof the white binders in the water. This results in a binder/watermixture.

Separate out ⅓ by volume of the previously prepared binder/water mixtureinto a separate container to be set aside and used later at the end ofthe mixing process.

To the ⅔ binder water mixture remaining in the mixing container, addapproximately 50 lbs of the mineral extender, preferably kaolin clayhaving a median particle size of about 2 microns. Agitate the mixtureuntil a thick paste is formed. Continue to agitate themineral/binder/water paste for 20 to 30 minutes until all of the mineralextender is mixed in and a smooth paste results.

To the mineral/binder/water paste obtained above, slowly add whilemixing, approximately 6.28 lbs. of the acrylic binder emulsioncontaining the calcium carbonate buffering agent and the titaniumdioxide pigment component.

To the mixture just obtained above, add slowly approximately 1.36 lbs.of the defloculant, preferably sodium silicate. The defloculant shouldbe divided and added in 3 parts, each time mixing until the defloculantis completely dispersed in the paste.

After addition of the defloculant, add slowly and with agitationapproximately 0.04 lbs of surfactant to the mixture.

To the mixture just obtained above, add slowly and with agitation, theremaining ⅓ of the binder/water mixture that was set aside as set forthabove.

The sealer coat 61 which is preferably a styronenated acrylic emulsionallows the coating composition 62 to remain pH neutral, for whateveracidity that resides in the backing material 60 is not allowed to leachthrough to the coating composition 62. Not only is it desirable that theclay mixture remain pH neutral to eliminate unwanted chemical reactionswith the artist's pigments or colors, the various layers that constitutethe scratchboard of the present invention would tend to separate due toformation of salts between the backing and the clay mixture coating as aresult of chemical reactions.

Next, the mineral extender component of the coating composition 62 ispassed through a mesh screen to filter out discontinuities.“Discontinuities,” for purposes of the present invention, is defined asbubbles, debris, lumps of undissolved clay or other incompletely mixedingredients present in the mixture. The mesh screen further mixes thesolution.

The use of a neutral sealer coat further (1) prohibits the backingboard's color from soaking through from beneath, (2) permits the use ofwater-based media without fear of the water soaking through to thebacking and (3) allows the addition of photosensitive chemicals on thesurface for photographic purposes without chemical reactions takingplace.

In a preferred embodiment of the present invention, the coatingcomposition can be applied over the sealer coat to achieve differentcharacteristics for the coating composition. First, the coatingcomposition can be deposited on hardboard sealed on the mineral coatedside with sealer coat, and offered with the original surface (as itcomes off the drying rack), a random orbital sanded surface using 220grit, and a sandblasted surface using 120 grit abrasive; and cut tovarious standard frame sizes and edge dressed. This produces thescratchboard structure found in FIG. 6.

Second, the coating composition can be deposited on hardboard sealed onboth sides and on the edges to enable immersion in water orphotochemicals without leaching of chemicals and stain from thehardboard. In accordance with this second embodiment of the presentinvention, uses for photographic printmaking offer many new advantagesto the photographer, principal of which is a more physically durable andchemically inert printing plate of enhanced permanence, a reworkableprint after printing with scratching tools and paint application, aprint surface of large size capability, and ease of framing withoutglass. The advantages of this second embodiment that distinguish it fromthe prior art is the immersibility required for the developing andfixing baths, particularly with the use of the acrylic plasticsupporting base, and, the whiter surface than the prior art 6 tilekaolin scratchboard without the pit defects. This produces theembodiment found in FIG. 9.

Third, the coating composition can be deposited on {fraction (3/64)}inch acrylic plastic, the sealer coat and the alternative surfacetexturing techniques being the same as for the hardboard base support.In accordance with this embodiment of the present invention, themanufacturing process using acrylic plastic requires the modification ofsanding the side to be sealed with 100 grit paper on a random orbitalsander to give the slick surface tooth enough for good bonding of thesealer coat.

The advantages of this third embodiment of the present inventioninclude: (1) a clay surface on a flexible base support which, whenflexed into a bend of 4 inches in diameter or less will neither crackthe clay surface nor cause it to flake off the base support; and (2)total and repeated immersibility in water or photochemicals without lossof surface integrity when subsequently dried.

The embodiment just described above provides the illustrator an artboard with the surface qualities described above, but which can bereproduced using the drum-type laser printers in common use in theindustry. This embodiment also provides the photographer a printingplate with the qualities of permanence, reworkability, and, unlike thehardboard, a relatively lightweight print support. This produces theembodiment illustrated in FIG. 10, wherein the backing material 60 is asemi-rigid plastic material. The plastic may be acrylic, styrene,polyvinyl chloride or other similar materials. Note that the sealer coat61 is not employed to chemically isolate the backing material 60 fromthe coating composition 62, but rather to provide proper surfacecharacteristics for bonding of the coating composition 62 to the backingmaterial 60 (as with a primer).

Fourth, a clay surface containing a combination of expanded ground,perlite (SiO₂ and AlO₂) and coating composition 62 can be deposited onthe sealer coat 61.

The advantage of this alternative embodiment is, for watermedia artistsprimarily, provision of an art surface with the advantages describedabove, though with more limited reworkability with scratching andscraping tools than the clay-only scratchboard (but certainly more thanpaper), but with a water-absorbing quality similar to watercolor paper.This allows the artist to execute transparent washes in a conventionalway in addition to performing opaque work with water media. Further, thechemical composition of the perlite is notably stable under theinfluence of acids, alkalies and exposure to ultraviolet rays, thusenhancing the stability of pigments on the surface and thus directlyenhancing the permanence of the artwork.

Thus, this alternative embodiment makes use of some of the features ofthe first embodiment, namely permanence of the clay surface on asupporting base, repeated immersibility or wetting ability, greaterchoice of larger sizes, a modified formulation of binder appropriate forthe addition of the expanded perlite. New to the prior art, by virtue ofthe addition of the expanded perlite, is a coating surface whichapproximates the absorbent surface of water color paper. This producesthe embodiment illustrated in FIG. 8, wherein the perlite is entrainedin the clay coating 62.

Fifth, a coating surface 62 the same as in the fourth embodiment, above,can be deposited on the sealer coat 61, but with the addition of acoarser grade of expanded, ground perlite grit to the surface effectedby coating the clay surface with a diluted adhesive and evenlydistributing the perlite onto the wet adhesive.

This fifth alternative embodiment provides a coating surface of moreabrasive quality on the surface yet with a layer softness, by virtue ofthe added expanded perlite, a soft absorbent material in the clay layer,thus approximating the tactile qualities of paper. These features are ofmost advantage to pastel artists to whom the resilient touch of thesurface is important in the control of the “stroke” they are able toexecute. The added abrasiveness of the surface by virtue of the addedexpanded perlite facilitates the “pulling off” of pigment from thepastel stick as well as the adhesion of the powdered pigment to thesurface. This surface may be scratched back into to a somewhat lesserdegree than with the clay-only scratchboard, but offering the pastelartist, for the first time, the scratchboard advantage in working withdry pigments. This produces the embodiment found in FIG. 7, wherein theexpanded perlite grit is shown as a plurality of particles 70 depositedon the coating composition 62.

Important to note is that these coatings can be applied to surfacesother than a rigid backing material, e.g., interior walls, furniture,wooden and unglazed ceramic objects to create sculpture withscratchboard surface qualities.

In accordance with the objectives of this invention, to improve upon theprior art from an artistic use standpoint and to create new media forartistic expression, the features of these preferred embodiments attackthe problems of permanence, versatility of use, quality of the surfaces,innovation of new clay surfaces and health hazard to factory workers andusers of the product.

Turning now to FIG. 7, illustrated is an isometric cutaway view of thepresent invention as modified to function as a pastel board. The abilityto coat the above “watercolor board” with an abrasive coating of fineperlite sand particles 70 provides a surface for pastel and charcoalartists that has the unique feature of “feeling soft to the touch” likepaper, the preferred based for pastel except for paper's notoriousimpermanence.

Turning now to FIG. 8, illustrated is an isometric cutaway view of thepresent invention as modified to function as a watermedia board. Theability to incorporate the clay perlite in its expanded form along withthe coating composition provides a surface approximating the texture andabsorbency of water color paper allowing conventional water mediatechniques including transparent washes with the permanence, and otheradvantages of the clay surface on a supporting base.

Turning now to FIG. 9, illustrated is an isometric cutaway view of thepresent invention as modified to function as a photographic board. Thesealer coat 61 has been extended to completely surround the backingmaterial 60. This allows the scratchboard to be completely immersed influid without fear of wetting the backing material 60. Followingaddition of a layer of coating composition 62, a layer of photosensitivematerial 90 is applied by conventional deposition techniques in adarkened room.

Turning now to FIG. 10, illustrated is an isometric cutaway view of thepresent invention as modified to function as a laser printer board. Thecoating composition of the present invention provides the sufficientdegree of flexibility to allow the coating composition to be bent in acurve when dried. The ability to apply the coating composition of thepresent invention as a surface to a {fraction (1/16)}″ plasticsupporting base allows, by virtue of the improved binder formula greaterflexibility to the coating composition 62, and adhesion to the base,allowing artwork to be reproduced in the widely used drum-type laserprinters requiring the original art work to be bent around the drum, aswell as providing an immersible, lighter weight photoplate.

Turning now to FIG. 11, illustrated is a block diagram of a preferredmethod of manufacturing an artistic media using the coating composition62 of the present invention. The method begins at a start block 110wherein the backing material has been readied for application of thesealing coat. The substrate to be coated (e.g., hardwood, acrylic,glass, metal, etc.) is fed into the front of a conveyor. Then, thesealing coat is applied to the backing material in step 111.

The use of a sealer coat on the supporting base provides: (1) a moreeffective block to ion transfer from the acidic hardboard backing to thecoating composition surface than in the prior art 6 tile kaolinscratchboard which used diluted adhesive, insuring art pigment stabilityover time, a consideration critical for fine art permanence, (2) lessdarkening and color change in the wetted coating composition surfaceduring watermedia applications than the old 6 tile kaolin scratchboarddue to dark hardboard color “show-through” because of saturation down tothe board surface, (3) better bond to the coating layer, (4) a smoother,more impermeable base for the coating composition which results in asmoother dried coating, requiring no further elaboration for artisticuse and (5) when coated on the back and edges, as well, provides totalimmersibility without chemical leaching from the hardboard, ofphotoprint developing importance.

In addition, the sealer coat allows for a correspondingly smooth surfacecoating, making smooth application critical to quality in the surfacecoat. In addition, the sealer coat provides a more than adequate bondbetween it and the coating composition surface, witnessed by anadherence test, in which the material is subjected to repeated blows,coating surface side up, on a hard edged object such as a table edge,looking for separation along the surface coating/sealer coat interface.In addition, the sealer coat acts as an impermeable block to watersaturation of both the sealer coat and the hardboard surface underneath,in the described embodiment, thus preventing the dark color of wethardboard to show through the sealer coat or through the wettablesurface coat which would register as a color and value change on thecoating surface when wetted in normal application of water bornepigments, the same holding true for oil-borne pigments. Next, thesealing coat is dried in ovens in step 112. This prepares the backingmaterial for deposition of the clay mixture in step 113.

The selection of a clay, a delaminated kaolin, (AlO₂ and SiO₂) is bothchemically and physically refined compared to both tile 6 kaolin andEnglish-mined China (also a kaolin).

The delaminated kaolin clay's lack of impurities, extremely uniformparticle size and the separateness of the individual clay plateletsprovide: (1) a whiter surface than 6 tile, and an equally white surfaceas the coating of Dickson but warmer in color, particularly when wetted,due to lack of mica particles which are bluish in color, (2) a smootherand more uniform surface allowing scratching and scraping strokes ofmore control than with the prior art, (3) a lack of surface pits therebyproviding a smooth surface and preventing the appearance of dark spotsin artwork, an improvement in quality (particularly in pen and inkwork), (4) a materials savings due to decreased amount of binderrequired (½ the binder as with prior art 6 tile kaolin scratchboard),(5) a cost advantage in reduced drying time due to the delaminatedkaolin requiring less water for a given viscosity (⅖ less water than theprior art 6 tile kaolin scratchboard), (6) an improvement of shelf lifeover unrefined clays due to its particles maintaining a uniformdispersion in the glue/water mix over a longer period of time, (7) anelimination of a health hazard to factory workers as well as artists dueto lack of silicosis caused by quartz particles in the clay dust, unlikeall other prior art and (8) a more uniform curtain formation. This iscritical when using a curtain applicator.

The manner in which the clay mixture is applied is critical to producingthe product because of the thickness of the clay mixture and the need toproduce these products on a mass scale. One preferred feature, then, isthe novel adaptation of existing coating technologies to the needs ofthe invention including, a curtain coater for the clay surfaceapplication and a bank of drying ovens to accelerate the drying process,all along a single conveyor thus greatly increasing the speed andquality control over the prior art. The curtain coater can be, forinstance, an Ashdee Curtain Coater manufactured by George Koch Sons,Inc..

The advantages of this one-coat method of clay surface application overwhat is used for the prior art, i.e., consecutive sprayed applicationsof material on the base support, has the advantages of greater speed,less maintenance to achieve consistency, more flexibility in its abilityto handle various types of base supports of various sizes up to 4 feetby 8 feet and in its ability to easily adjust coat thicknesses. In priorart, only a limited thickness has been achieved due to the sprayingtechnology used.

The backing material, either hardboard or acrylic plastic or other rigidor semi-rigid supporting base, passes through the curtain coater wherethe clay coat is deposited and then immediately enters the main dryingovens. The ovens provide an initial amount of drying before the panelsare stacked in drying racks at the end of the conveyor line, thusshortening the stack drying time by approximately two thirds. In thealternative, the ovens can eliminate stack time by completely drying thesurface. The forced air covens also provide the necessary function ofridding the wet clay layer of bubbles which would otherwise result inunwanted pits in the finished dry surface.

Next, the curtain-applied clay mixture is partially or completely driedin ovens in step 114. Applying an oven-drying process reduces dryingtime and eliminates pit-causing bubbles in the wet clay layer whilepassing through the ovens. The freshly-coated clay mixture goes directlyinto drying ovens. The bubbles, when heated in the ovens, expand, riseto the surface and burst leaving the dried clay surface completely freeof the unwanted pits and latent bubbles, a definite improvement insurface quality over the prior art, all of which display varying amountsof pit defects.

Next, the surface textures are stacked and air dried in step 115. Stackdrying times vary with the size of panels, the type of panel, the amountof air circulation, either natural or mechanically induced, the claysurface thickness, and the relative environmental humidity. Two totwelve hours is usually adequate.

Next, optional surface textures are applied in step 116. Optionalsurface treatments may be performed including: (1) sanding with variousgrits and with various apparatus to give the clay surface a variety ofsanded textures, including a random orbital pattern using apneumatically-driven palm sander with at least 10,000 orbits per minute,(2) achieving a cross-sanded pattern which simulates a linen-liketexture on the surface achieved with a belt sander of variousalternative configurations applied to the surface first in one directionfollowed by a direction 90° from the first, (3) any other hand orappliance type sanding method applied at the discretion of the artist inthe studio or (4) sandblasting the surface, again with various giftsizes from 220 grit to 50 grit, accomplished in a blasting cabinet orroom with either a simple suction feed or pressure feed sandblaster.

Many other alternative methods may be used to texture the clay surfaceincluding several used in prior art such as pressing a textureconfiguration into the surface with templates made of stone, metal,plastic fiber, etc. In accordance with the present invention, a physicalproperty of the clay surfaces of this embodiment which facilitatespressing a texture configuration into the surface is that, when wettedin a uniform manner, the clay coat is temporarily softened facilitatingthe imprint. When it is subsequently dried, the integrity of theoriginal surface returns, and the process then ends in end block 117.

EXPERIMENTAL RESULTS

Two different experiments (a wet abrasion resistance test and aflexibility test) were conducted on three different coatingcompositions, including the coating composition of the presentinvention. The coatings are: the present composition (PC), 6 Tile Koalin(6TK) and the Dickson coating (DC).

Wet abrasion resistance is defined herein is the surface's resistance toscratching or scoring with a sharp object. The testing apparatus wascomprised of three #16 needles affixed to a weight platform made of woodor other suitable flat support. The needles were arranged in the centerof the board in an 8″ diameter circle extending downwardly from thebottom of the platform by ½″. Weight was added to the top side of theplatform until the combined weight of the apparatus was 3.5 pounds (1.5Kg).

The weighted platform was then gently placed on the respective wet claycoatings with the needles bearing the weight of the platform and cominginto contact with the clay surface. The platform was then pulled acrossthe coating surface at a constant velocity of 1 ft/sec. As the devicewas pulled across the respective coating surfaces, it took more forcefor the needles to pull the clay off the substrate in the presentcomposition as compared to the other compositions. The amount of forcenecessary was measured with the results as follows:

The PC coating required 1.5 to 1.7 Kg of force to pull the platformacross the coating surface; the PTK coating required 1.5 to 1.7 Kg offorce to pull the platform across the coating surface and the DC coatingrequired 0.3 to 0.4 Kg of force to pull the platform across the coatingsurface.

The second test that was conducted was the flexibility test that wasconducted in an environment having 10% relative humidity or less. Therespective coatings were applied to a thickness of approximately 20 milson a 3 mil thick sheet of flexible plastic and allowed to dry. A 1 inchstrip approximately 10 inches long of the coated flexible plastic wascut from each sample. The strips were dried in an oven until the coatingmoisture content was 5% or less. The dried strip were then graduallybent into reducing diameter circles until the first cracked appeared andthe resulting diameter was noted. This was repeated three time for eachsample and an average was taken with the results as follows:

The PC coating could be bent into a circle having a diameter rangingbetween 2 inches to 3 inches in diameter without cracking. The 6TKcoating could be bent into a circle having a diameter of 12 incheswithout cracking and the DC coating could be bent into a circle having adiameter of 12 inches without cracking. Thus as seen, the coatingcomposition of the present invention has a much higher degree offlexibility.

From the above, it is apparent that the present invention provides amineral-based coating composition, a method of making that compositionand a method of making an artistic medium using the coating of thepresent invention.

Although the present invention and its advantages have been described indetail in the foregoing detailed description, those skilled in the artshould understand that the detailed description is given by way ofillustration only and that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined and limited solely by the appendedclaims.

What is claimed is:
 1. Media for artistic expression produced by aprocess, comprising: providing a mineral-based coating compositioncomprising a kaolin clay, mica, talc, montmorillonite atapulgite,illite, bentonite or halloysite mineral extender, water, a polyvinylacetate emulsion and an acrylic polymer binder; applying a sealing coatto a backing material; applying an at least about 20 wet mil layer ofsaid mineral-based coating composition over said sealing coat; anddrying said applied mineral-based coating composition to produce mediafor artistic expression.
 2. The media of claim 1 wherein said mineralextender comprises from about 20% to about 36% of said coatingcomposition's total weight, said water comprises from about 40% to about60% of said coating composition's total weight, said polyvinyl acetateemulsion comprises from about 16% to about 24% of said coatingcomposition's total weight and said acrylic polymer binder comprisesfrom about 2% to about 5% of said coating composition's total weight. 3.The media of claim 1 wherein said polyvinyl acetate emulsion is ahomopolymer polyvinyl acetate emulsion and a co-polymer polyvinylacetate emulsion.
 4. The media of claim 3 wherein said homopolymerpolyvinyl acetate emulsion comprises from about 13% to about 18% of saidcoating composition's total weight and said co-polymer polyvinyl acetateemulsion comprises from about 3% to about 6% of said coatingcomposition's total weight.
 5. The media of claim 1 wherein said acrylicpolymer binder further comprises a pigment and a buffering agent.
 6. Themedia of claim 1 wherein said mineral-based coating composition has a pHof from about 7.0 to about 7.5.
 7. The media of claim 5 wherein saidpigment is selected from the group consisting of titanium dioxide,zirconium dioxide and hafnium dioxide.
 8. The media of claim 5 whereinsaid pigment is titanium dioxide.
 9. The media of claim 1 wherein saidmineral-based coating composition is applied by a curtain coatingprocess.
 10. The media of claim 1 produced by a process furthercomprising the step of applying additional optional topical coatingsover said mineral-based coating.
 11. The media of claim 1 wherein saidbacking material is hardboard.
 12. The media of claim 1 wherein saidbacking material is plastic.
 13. The media of claim 1 wherein saidbacking material is acrylic plastic.
 14. The media of claim 1 whereinsaid mineral extender is kaolin clay.
 15. The media of claim 14 whereinsaid kaolin clay is a delaminated hydrated aluminum silicate clay havingan aspect ratio of about 11 to
 1. 16. The media of claim 1 wherein saidbacking material is flexible.
 17. The media of claim 1 wherein saidmineral-based coating composition further comprises a nonfoamingsurfactant.
 18. The media of claim 1 wherein said mineral-based coatingcomposition further comprises a defloculant.
 19. The media of claim 18wherein said defloculant is sodium silicate.
 20. The media of claim 1wherein said mineral-based coating composition further comprises watermiscible perlite.
 21. The media of claim 1 produced by a process furthercomprising the step of applying a perlite layer over said mineral basedcoating composition.
 22. The media of claim 1 produced by a processfurther comprising the step of applying a layer of photosensitivematerial over said mineral based coating composition.
 23. The media ofclaim 1 where the drying step comprises heating.
 24. An artistic mediumcomprising: a backing; and an at least 12 mil coating on said backing ofmineral-based composition comprising a kaolin clay, mica, talc,montmorillonite, atapulgite, illite, bentonite or halloysite mineralextender, a polyvinyl acetate emulsion and an acrylic polymer binder.25. An artistic medium for pastel artists, comprising: a backing; and anat least 12 mil coating on said backing of mineral-based compositioncomprising a kaolin clay, mica, talc, montmorillonite, atapulgite,illite, bentonite or halloysite mineral extender, a polyvinyl acetateemulsion and an acrylic polymer binder; and perlite grit adhering to thesurface of the coating.
 26. An artistic medium for watercolor artistscomprising: a backing; an at least 12 mil coating on said backing ofmineral-based composition comprising a kaolin clay, mica, talc,montinorillonite, atapulgite, illite, bentonite or halloysite mineralextender, a polyvinyl acetate emulsion, an acrylic polymer binder andperlite particles.
 27. An artistic medium for pastel or charcoal artistscomprising: an at least 12 mil coating on said backing of mineral-basedcomposition comprising a kaolin clay, mica, talc, montmorillonite,atapulgite, illite, bentonite or halloysite mineral extender, apolyvinyl acetate emulsion, an acrylic polymer and perlite particles;and perlite grit adhering to the surface of the coating.
 28. The mediumof claims 24, 25, 26 or 27 wherein the backing has a sealing coat.